Lecture 11: Regeneration

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Questions and Answers

What is the primary function of the transplanted hypostome in a host hydra?

It acts as an organizing center, signaling the host’s cells. (correct)

It provides nutrients to the host tissue.

It regenerates and becomes part of the host's structure.

It replaces damaged tissues in the host.

What occurs if the head inhibition gradient is eliminated in a hydra?

Tissue from below the head can form a new head structure. (correct)

No new heads can form regardless of tissue placement.

The hydra will regenerate only the foot structures.

It will result in uncontrolled growth of multiple heads.

Which signaling proteins are primarily responsible for head formation in hydra?

FGF signals

Hedgehog proteins

Wnt proteins (correct)

Notch signals

What effect does transplanting the basal disc into a recipient hydra have?

It leads to the growth of another basal disc. Signup and view all the answers

What characterizes the head activation gradient in hydra?

It is strongest near the head and diminishes towards the body. Signup and view all the answers

What is the first step that occurs in limb regeneration after amputation?

Formation of the Apical Ectodermal Cap Signup and view all the answers

What happens to cells after they de-differentiate during the regeneration process?

They lose their specialized functions and become more like stem cells. Signup and view all the answers

Which statement is true regarding the positional values of cells during limb regeneration?

Cells retain a memory of their original location along the proximal-distal axis. Signup and view all the answers

What determines whether all parts or only distal parts are regenerated?

The location of the amputation along the limb. Signup and view all the answers

What role do macrophages play in limb regeneration?

They are involved in wound healing. Signup and view all the answers

What is the sequence of events that occurs during the limb regeneration process?

De-differentiation, proliferation, re-specification. Signup and view all the answers

Which component is essential for the formation of a blastema during regeneration?

Apical Ectodermal Cap Signup and view all the answers

What is essential for proper limb regeneration in organisms such as newts?

Complete nerve supply Signup and view all the answers

Which growth factor is secreted by anterior cells to aid limb regeneration?

Fibroblast Growth Factor 8 Signup and view all the answers

What occurs if the nerve is removed from an amputated limb?

Regeneration is incomplete Signup and view all the answers

What is the role of Nerve Anterior Gradient Protein (NAG) in limb regeneration?

It is only effective when nerves are present Signup and view all the answers

How does the process of limb regeneration occur in salamanders after amputation?

Regeneration occurs in a distal direction Signup and view all the answers

What happens when a limb is amputated and inverted?

Distal structures still develop in regeneration Signup and view all the answers

What must be present in the blastema for proper limb regeneration?

Both anterior and posterior cells Signup and view all the answers

What is the relationship between FGF8 and Sonic Hedgehog in limb regeneration?

FGF8 stimulates Sonic Hedgehog and vice versa Signup and view all the answers

What dictates the outcome of limb regeneration after an amputation?

The location of the cut Signup and view all the answers

What is the primary role of Prod1 in limb regeneration?

Providing positional information for regeneration Signup and view all the answers

How do the motility and adhesiveness of proximal and distal tissues differ?

Proximal tissue is less adhesive and more motile Signup and view all the answers

What effect does blocking Prod1 with an antibody have on the proximal blastema?

Inhibits the movement of the proximal blastema Signup and view all the answers

In the context of limb regeneration, what does 'positional value' primarily refer to?

The graded signal related to cell adhesiveness Signup and view all the answers

Which of the following statements about distal blastema cells is true?

They retain their positional memory in transplantation Signup and view all the answers

What happens when a distal blastema is grafted onto a proximal stump?

The proximal stump takes precedence in regeneration Signup and view all the answers

Which of the following components is essential for the interaction with Prod1 in limb regeneration?

NAG (nerve anterior gradient protein) Signup and view all the answers

What characteristic of proximal cells aids them in regeneration?

Greater levels of Prod1 expression Signup and view all the answers

What outcome is observed when the proximal blastema wraps around the distal blastema?

Proximal cells exhibit greater motility than distal cells Signup and view all the answers

Which of the following best describes the relationship between proximally and distally located cells during regeneration?

Proximal cells generally determine the nature of regenerated structures Signup and view all the answers

What is the role of the proximal blastema during limb regeneration?

To regenerate proximal structures such as the humerus and radius. Signup and view all the answers

Which signaling molecules are crucial for the formation of the blastema in limb regeneration?

FGF8 and Shh. Signup and view all the answers

How does the distal blastema differ from the proximal blastema?

It regenerates distal structures, including hand-like features. Signup and view all the answers

What is the direction of regeneration in salamanders?

Proximal to distal. Signup and view all the answers

What role does the nerve-derived factor nAG play in limb regeneration?

It influences the proliferation of blastema cells. Signup and view all the answers

Which germ layers are present in hydra?

Ectoderm and endoderm. Signup and view all the answers

What is the primary method of reproduction in hydra?

Asexual reproduction via budding. Signup and view all the answers

What is the significance of Prod1 expression during regeneration?

It defines positional values for tissue types at the cut site. Signup and view all the answers

What characterizes the hydra's continuous cell growth?

Cells constantly migrate along the body structure. Signup and view all the answers

Which of the following statements about limb regeneration is false?

Only distal structures can regenerate outside of their blastema. Signup and view all the answers

Study Notes

Regeneration Overview

Regeneration is the reactivation of developmental processes to restore lost tissues in post-embryonic tissues.
Regeneration types include physiological regeneration and epimorphosis and morphallaxis.

Physiological Regeneration

Normal process where stem cells regenerate lost cells.
Examples include: human hair shedding, skin renewal, and blood regeneration in humans, and annual antler regeneration in deer.

Epimorphosis

De-differentiation of adult cells to form an undifferentiated mass (blastema).
This blastema then re-specifies into the missing tissue.
Involves significant cell proliferation.
Examples include salamander/axolotl limb regeneration.

Morphallaxis

Regeneration through re-patterning existing cells, with minimal cell proliferation.
Examples include Hydra regeneration when cut in half, and compensatory mechanism in mammalian liver regeneration, and zebrafish heart.

Limb Regeneration in Amphibians

When a salamander limb is amputated, the remaining limb cells de-differentiate, forming a blastema.
Cells retain their positional value.
Through epimorphosis, cells re-differentiate to reconstruct the missing limb.
Distal amputation regenerates only the distal parts, while proximal amputation regenerates all parts relative to the body axis.
Regeneration involves de-differentiation, proliferation, and re-specification of cells.
Cells in blastema retain memory of their original tissue type and re-differentiate to form new limb parts.

Process of Limb Regeneration

Injury/amputation triggers a series of events, like macrophage infiltration and formation of an apical ectodermal cap.
De-differentiation leads to multi-potent progenitor cells.
Proliferation of cells forming the blastema.
Re-specification and regeneration of blastema cells for missing parts.

Factors Affecting Limb Regeneration

Apical Ectodermal Cap (AEC) plays a crucial role.
- Secretes FGF8, critical for blastema growth.
Limb regeneration depends on nerve supply.
- NAG from nerves promotes regeneration.
- Denervated limbs do not regenerate properly.
Cross-induction of FGF8 and Sonic Hedgehog (Shh) signals facilitates the regeneration process.

Positional Values in Regeneration

Positional values in regenerating limbs involve graded signals related to cell adhesiveness and motility.
Proximal tissue is more motile, while distal tissue is more adhesive.

Prod1's Role in Limb Regeneration

Prod1 is a small glycolipid-anchored protein.
It interacts with nerve anterior gradient protein (NAG).
Expression is graded along the proximal-distal axis, with higher levels in proximal regions, which is important for positional information.
Graded expression is critical for regeneration of distal structures based on their positional information,

Hydra Regeneration

Hydra is a simple invertebrate with ectoderm and endoderm.
Regenerates lost structures (head or foot) via cell repatterning.
Regeneration is polarised.
Head/Foot are organizing centers for new structure formation.
Head inhibition gradient prevents extra head formation.

Heart Regeneration in Zebrafish

Adult zebrafish can regenerate damaged heart.
Epidermis forms a clot and cell migration occurs.
New cardiac tissue develops.
Fibroblast growth factors (FGFs) signal epicardial cells for migration into damaged areas and new muscle formation.
Cardiomyocytes undergo limited dedifferentiation during regeneration

Regeneration in Various Organisms

Zebrafish and salamanders can regenerate entire hearts or limbs.
Rodents have limited heart regeneration capacity.
Humans have very little to no heart regeneration capacity.

Transgenic Approaches

Scientists explore how regenerative genes in mammals may induce heart regeneration.

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Description

Explore the fascinating processes of regeneration in biological systems, including physiological regeneration, epimorphosis, and morphallaxis. Learn about the mechanisms behind tissue restoration in various organisms, from humans to amphibians. Discover how stem cells and other cellular processes contribute to regrowth and repair.